Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A receiver includes: a measurement unit configured to measure received
power of a pilot signal symbol included in a received signal and generate
a received power measurement value for each of a plurality of measurement
periods; and a calculator configured to calculate received power by
calculating a weighted average of a plurality of received power
measurement values obtained by the measurement unit based on the numbers
of the pilot signal symbols that are included in respective measurement
periods.

Claims:

1. A receiver comprising: a measurement unit configured to measure
received power of a pilot signal symbol included in a received signal and
generate a received power measurement value for each of a plurality of
measurement periods; and a calculator configured to calculate received
power by calculating a weighted average of a plurality of received power
measurement values obtained by the measurement unit based on the numbers
of the pilot signal symbols that are included in respective measurement
periods.

2. The receiver according to claim 1, wherein the calculator calculates
the received power by calculating the weighted average of the plurality
of received power measurement values using the numbers of the pilot
signal symbols that are included in respective measurement periods as
weights of the weighted average calculation.

3. The receiver according to claim 1, wherein the calculator calculates
the received power by calculating the weighted average of the plurality
of received power measurement values using squares of the numbers of the
pilot signal symbols that are included in respective measurement periods
as weights of the weighted average calculation.

4. The receiver according to claim 1 further comprising a weight
coefficient calculator configured to calculate a weight coefficient of
each received power measurement value so that a received power
measurement value corresponding to a measurement period including a
larger number of pilot signal symbols is assigned a larger weight,
wherein the calculator calculates the weighted average of the plurality
of received power measurement values using the weight coefficient
calculated by the weight coefficient calculator to obtain the received
power.

5. The receiver according to claim 4, wherein the weight coefficient
calculator calculates the weight coefficient according to information
about an allocation of pilot signal symbols received from a base station
connected to the receiver.

6. A method for measuring reception quality by a receiver, the method
comprising: measuring received power of a pilot signal symbol included in
a received signal for each of a plurality of measurement periods to
generate a plurality of received power measurement values; and detecting
reception quality by calculating a weighted average of the plurality of
received power measurement values based on the numbers of the pilot
signal symbols that are included in respective measurement periods.

7. A terminal equipment comprising: a receiver circuit configured to
receive a signal that includes a pilot signal symbol from a base station;
and a processor configured to process the received signal, wherein the
processor measures received power of the pilot signal symbol included in
the received signal for each of a plurality of measurement periods to
generate a plurality of received power measurement values, and the
processor detects reception quality by calculating a weighted average of
the plurality of received power measurement values based on the numbers
of the pilot signal symbols that are included in respective measurement
periods.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based upon and claims the benefit of priority
of the prior Japanese Patent Application No. 2012-215171, filed on Sep.
27, 2012, the entire contents of which are incorporated herein by
reference.

FIELD

[0002] The embodiments discussed herein are related to a receiver and a
reception quality measurement method used in a wireless communication
network.

BACKGROUND

[0003] Recently, with an increasing amount of data in wireless
communications, a mobile communication system has been put into practical
use using orthogonal frequency division multiple access (OFDMA) for
realizing high frequency utilization. In the third generation partnership
project (3GPP), as one of the mobile telephone systems, the
standardization of long term evolution (LTE) has been completed, and a
standard specification of LTE-advanced, which is a enhanced scheme of
LTE, has been studied.

[0004] In LTE and LTE-advanced, orthogonal frequency division multiplexing
(OFDM) is adopted in the downlink (DL) for transmitting a signal from a
base station to a terminal equipment (mobile station etc.), and single
carrier frequency division multiple access (SC-FDMA) is adopted in the
uplink (UL) for transmitting a signal from a terminal equipment to a base
station.

[0005] A downlink signal transmitted from the base station includes a
pilot signal. The terminal equipment measures the reception quality of
the signal transmitted from the base station using the pilot signal. The
pilot signal is called a reference signal (RS) in LTE and LTE-Advanced.

[0006] When there are a plurality of base stations, the terminal equipment
measures the reception quality corresponding to each base station
according to the pilot signal received from each base station. The
measurement result may be reported to the base station which is connected
to the terminal equipment (called "serving cell"). The base station which
accommodates the terminal equipment decides based on the measurement
result a base station to which the terminal equipment is to be connected.
In this case, a handover is performed as necessary.

[0007] Proposed as one of the related techniques is a configuration
capable of measuring signal to interface ratio (SIR) with high accuracy
in the mobile communication system based on code division multiple access
(CDMA) even when abrupt interference occurs. Another related technique
proposed is a SIR measurement device capable of measuring SIR with high
accuracy in a wide range (for example, Japanese Laid-open Patent
Publication No. 2004-320254 and Japanese Laid-open Patent Publication No.
2005-12656). In addition, the specifications above are described in, for
example, 3GPP TS 36.211 V9.1.0, and 3GPP 36.214 V9.2.0.

[0008] A well-known method for suppressing noise in measuring the
reception quality is to calculate an average of a plurality of pilot
signals obtained in a specified length of measurement period. In this
case, when the measuring time is long, the noise is sufficiently
suppressed. However, for example, when the terminal equipment is mobile,
the terminal equipment may be incapable of correctly measuring the
reception quality with long measurement time.

[0009] The terminal equipment may measure reception quality in each of a
plurality of short periods and calculate a weighted average of the
measurement results based on propagation environment. In this method, an
error caused by a movement of the terminal equipment may be suppressed.
In this case, the terminal equipment estimates as a propagation
environment, for example, the number of significant paths, a standard
deviation of desired wave power, a standard deviation of a SIR, a Doppler
frequency, etc. However, it is difficult to estimate the propagation
environment constantly with high accuracy. Therefore, when the estimation
accuracy of the propagation environment is low, the reliability of the
measurement result of the reception quality is also reduced. Furthermore,
since the process of estimating the propagation environment is subject to
computational complexity, there is the possibility of large power
consumption in the terminal equipment.

SUMMARY

[0010] According to an aspect of the embodiments, a receiver includes: a
measurement unit configured to measure received power of a pilot signal
symbol included in a received signal and generate a received power
measurement value for each of a plurality of measurement periods; and a
calculator configured to calculate received power by calculating a
weighted average of a plurality of received power measurement values
obtained by the measurement unit based on the numbers of the pilot signal
symbols that are included in respective measurement periods.

[0011] The object and advantages of the invention will be realized and
attained by means of the elements and combinations particularly pointed
out in the claims.

[0012] It is to be understood that both the foregoing general description
and the following detailed description are exemplary and explanatory and
are not restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

[0013] FIG. 1 illustrates an example of a wireless communication system in
which a receiver according to an embodiment of the present invention is
used;

[0014] FIG. 2 illustrates a structure of a downlink subframe;

[0015] FIG. 3 illustrates a configuration of a receiver according to an
embodiment of the present invention;

[0030] FIG. 18 illustrates the probability density function of RSRP
calculated in the method according to the first embodiment;

[0031] FIG. 19 illustrates the probability density function of RSRP
calculated in the method according to the second embodiment; and

[0032] FIGS. 20A and 20B illustrate examples of a handover operation based
on RSRP.

DESCRIPTION OF EMBODIMENTS

[0033] FIG. 1 illustrates an example of a wireless communication system in
which a receiver according to an embodiment of the present invention is
used. A wireless communication system 1 illustrated in FIG. 1 is not
specifically limited, but is supposed to support LTE and LTE-Advanced of
the 3GPP.

[0034] The wireless communication system 1 includes a plurality of base
stations 2 (2a, 2b). Each base station 2 may communicate with a terminal
equipment located in a cell. A cell refers to an area in which the base
station 2 can communicate.

[0035] Terminal equipment 3 is, for example, a mobile station such as a
mobile telephone terminal etc. The terminal equipment 3 may communicate
with one of the plurality of base stations 2. In FIG. 1, the terminal
equipment 3 communicates with the base station 2a.

[0036] Each base station 2 transmits a downlink signal to a terminal
equipment located in the local cell. In the downlink, OFDMA is used in
this example. Therefore, the terminal equipment 3 receives a downlink
signal from the base station 2a. Since the terminal equipment 3 is also
located in the cell of the base station 2b, the downlink signal
transmitted from the base station 2b also arrives at the terminal
equipment 3. The downlink signal transmitted from the base station 2 may
include a reference signal described later.

[0037] The terminal equipment 3 transmits an uplink signal to a serving
base station. In the example illustrated in FIG. 1, the base station 2a
operates as a serving base station for the terminal equipment 3. In this
case, the terminal equipment 3 transmits an uplink signal to the base
station 2a. In the uplink, SC-FDMA is used in this example. The terminal
equipment 3 reports the measurement result of the reception quality to
the serving base station.

[0038] FIG. 2 illustrates a structure of a subframe transmitted through
the downlink. In the downlink, data is transmitted using a plurality of
subcarriers of different frequencies. In FIG. 2, Nc refers to the number
of subcarriers of the downlink. The number of subcarriers may depend on
the communication bandwidth of the downlink. Each subcarrier may transmit
a modulated signal of QPSK (quadrature phase shift keying), 16QAM
(quadrature amplitude modulation), 64QAM d, etc.

[0039] One subframe is configured by Nsym OFDM symbols. An OFDM
symbol includes symbols transmitted through respective subcarriers. That
is, the OFDM symbol is configured by Nc symbols. Nsym is, for
example, 14. However, Nsym is not limited to 14. Furthermore, a
radio frame is formed by 10 consecutive subframes. The downlink subframes
of LTE and LTE-Advanced are described in 3GPP TS36.214 V9.2.0.

[0040] In the downlink, the base station 2 transmits a reference signal
(RS). The reference signal is an example of a pilot signal. The reference
signal is used in measuring the power of a signal received by the
terminal equipment 3 from the base station 2 in this specification, but
may be applied to other uses.

[0041] Reference signals are allocated at the intervals of 6 subcarriers
in one or more OFDM symbols in a subframe. In the example illustrated in
FIG. 6, Nc/6 reference signals are allocated at OFDM symbols #0, #4, #7,
and #11.

[0042] The reference signal is known to the base station 2 and the
terminal equipment 3. Therefore, when the reference signal transmitted
from the base station 2 is compared with the reference signal received by
the terminal equipment 3, the state of the propagation path between the
base station 2 and the terminal equipment 3 may be detected. For example,
since the transmitted power of the reference signal from the base station
2 is known, the state of the propagation path is detected by detecting
the received power of the reference signal in the terminal equipment 3.

[0043] While communicating with the base station 2, the terminal equipment
3 periodically measures the reception quality of each cell. In the
example illustrated in FIG. 1, while communicating with the base station
2a, the terminal equipment 3 measures the reception quality of the cell
of the base station 2a and the reception quality of the cell of the base
station 2b. Then, the terminal equipment 3 reports the measured reception
quality to the serving base station (base station 2a in this example). By
so doing, the serving base station determines the optimum cell for the
terminal equipment 3. If the cell of the base station other than the
serving base station is the optimum, the serving base station perform a
handover.

[0044] The reception quality reported from a terminal equipment to a base
station is, for example, a received signal strength indicator (RSSI),
reference signal received power (RSRP), reference signal received quality
(RSRQ), etc. This report is called "Measurement Report" in LTE and
LTE-Advanced.

[0045] FIG. 3 illustrates a configuration of a receiver according to an
embodiment of the present invention. A receiver 10 according to the
embodiment includes a radio frequency (RF) unit 11, a fast Fourier
transform (FFT) unit 12, a data receiver 13, and a measurement unit 16 as
illustrated in FIG. 3. The FFT unit 12, the data receiver 13, and the
measurement unit 16 are not specifically limited, but are realized by,
for example, a digital signal processor. However, the FFT unit 12, the
data receiver 13, and the measurement unit 16 may be realized by a
hardware circuit, or a combination of a hardware circuit and a digital
signal processor. The receiver 10 is implemented in the terminal
equipment 3.

[0046] The RF unit 11 converts a received signal input through an antenna
into a baseband digital signal. That is, the RF unit 11 converts an OFDM
signal transmitted from the base station 2 into a baseband digital
signal.

[0047] The FFT unit 12 transforms a time domain signal into a frequency
domain signal by FFT operation. That is, the FFT unit 12 generates a
frequency domain signal from the baseband digital signal output from the
RF unit 11. As a result, modulated signals transmitted through respective
subcarriers of the OFDM signal are obtained. For example, when a subframe
in the format illustrated in FIG. 2 is transmitted from the base station
2, the FFT unit 12 generates Nc modulated signals.

[0048] The data receiver 13 recovers transmission data from the frequency
domain signal output from the FFT unit 12. The data receiver 13 includes
a demodulator 14 and a decoder 15. The demodulator 14 demodulates the
frequency domain signal. That is, the demodulator 14 demodulates
respective modulated signals transmitted through the subcarriers. In this
case, the demodulator 14 may perform the demodulation using a result of
the channel estimation. Furthermore, the decoder 15 decodes a received
signal demodulated by the demodulator 14 to recover the transmission
data.

[0049] The measurement unit 16 measures or calculates the reception
quality of the downlink signal transmitted from the base station 2. The
reception quality measured or calculated by the measurement unit 16 is
RSRP, RSSI, and RSRQ. Therefore, the measurement unit 16 includes an RSRP
measurement unit 17, an RSSI measurement unit 18, and an RSRQ calculator
19.

[0050] The RSRP measurement unit 17 measures RSRP using the frequency
domain signal (that is, Nc modulated signals) output from the FFT unit
12. In this case, the RSRP measurement unit 17 measures the received
power of the reference signal symbol allocated in the subframe
illustrated in FIG. 2. The method for measuring RSRP is described below
with reference to FIGS. 4 and 5.

[0051] FIG. 4 illustrates an example of measuring RSRP when the terminal
equipment 3 remains stationary. The terminal equipment 3 estimates the
channel state between the base station 2 and the terminal equipment 3.
The channel state is expressed by a complex number. The complex number is
obtained by detecting the I and Q components of the received reference
signal.

[0052] The terminal equipment 3 estimates the channel state at time T1,
T2, and T3. In the embodiment, the terminal equipment 3 remains
stationary. Therefore, if it is assumed that there is no noise, the
channel state h remains unchanged during T1-T3 as illustrated in FIG. 4.

[0053] However, noise exists in the actual wireless communication system.
Therefore, the channel state estimated from the received reference signal
in the terminal equipment 3 is affected by the noise. In the example in
FIG. 4, the channel states h'1, h'2, and h'3 are
respectively detected at time T1, T2, and T3.

[0054] The RSRP measurement unit 17 suppresses the noise power by
averaging the received signals including the noise. The RSRP measurement
unit 17 then measures the received power according to the noise
suppressed signal. For example, when the channel states h'1, through
h'3 are obtained at time T1 through T3, respectively, the RSRP
measurement unit 17 first obtains the average channel state h' by the
following formula. The averaging operation is a complex average (voltage
average).

h'=(h'1+h'2+h'3)/3

[0055] Then the RSRP measurement unit 17 calculates the received power
Pest from the average channel state h' by the following formula.

Pest=|h'|2

[0056] Since the noise power is suppressed by the averaging operation, the
average channel state h' is approximate to the ideal channel state h.
Therefore, the received power Pest calculated from the average
channel state h' is approximate to the ideal value Pideal of the
received power. The received power Pest is output as RSRP indicating
the received power of the reference signal.

[0057] Note that the noise suppression effect becomes higher if the
averaging operation is performed by acquiring more reference signal
symbols in the time domain. That is, if the averaging time is longer, the
noise suppression effect becomes higher.

[0058] FIG. 5 illustrates an example of measuring RSRP while the terminal
equipment 3 is moving. When the terminal equipment 3 is moving, the
channel state changes with respect to time. That is, with the lapse of
time, the amplitude and/or phase of the received reference signal at the
terminal equipment 3 changes. Especially, while the terminal equipment 3
is moving at a higher speed, the channel state changes larger with
respect to time. In the example illustrated in FIG. 5, the channel states
h1, h2, and h3 are obtained respectively at time T1, T2,
and T3. Furthermore, since there is noise, the channel states estimated
at time T1, T2, and T3 are respectively h'1, h'2, and h'3.

[0059] In this case, when the above-mentioned averaging operation is
performed on the channel states h'1, h'2, and h'3, the
coordinates indicating the average channel state h' appears at the
position closer to the origin in the constellation than the actual
channel state as illustrated in FIG. 5. Therefore, the received power
Pest calculated from the average channel state h' is lower than the
ideal value Pideal of the received power.

[0060] Thus, when the terminal equipment 3 is moving at a high speed, the
error of RSRP indicating the received power of the reference signal
becomes large. The longer the averaging time is, the larger the error
becomes. Therefore, it is preferable that the averaging time for
measuring RSRP is appropriately determined considering both the noise
suppression and the error caused by the movement of the terminal
equipment 3.

[0061] Back in FIG. 3, the RSSI measurement unit 18 measures RSSI
indicating the strength of the received signal using the baseband digital
signal output from the RF unit 11. The RSRQ calculator 19 calculates RSRQ
indicating the quality of the reference signal from RSRP obtained by the
RSRP measurement unit 17 and RSSI obtained by the RSSI measurement unit
18. The details of the RSSI measurement and the RSRQ measurement are
omitted.

[0062] The measurement unit 16 reports RSRP and RSRQ obtained as described
above to the serving base station. By so doing, according to the report,
the serving base station determines the optimum cell of the terminal
equipment 3, and performs a handover as necessary.

[0063] FIG. 6 illustrates an example of a configuration of the RSRP
measurement unit 17. As illustrated in FIG. 6, the

[0064] RSRP measurement unit 17 includes a divider 21, a plurality of
measurement units 22 (22-1 through 22-n), a weight coefficient calculator
23, and a weighted average calculator 24. A received signal is fed to the
RSRP measurement unit 17. The received signal is a frequency domain
signal output from the FFT unit 12 (that is, Nc modulated signals).
Furthermore, the RSRP measurement unit 17 receives a control signal. The
control signal includes the information about the allocation of reference
signal symbols as described later in detail.

[0065] In the RSRP measurement unit 17, as illustrated in FIG. 6, the
divider 21, the plurality of measurement units 22, and the weight
coefficient calculator 23 operate according to the control signal.
Therefore, the control signal is first described below.

[0066] In LTE and LTE-Advanced, frequency division duplex (FDD) and time
division duplex (TDD) are supported as the methods of multiplexing an
uplink and a downlink. In FDD, the uplink communication and the downlink
communication are multiplexed by assigning different frequencies to the
uplink and the downlink. On the other hand, in TDD, the same frequency is
assigned to the uplink and the downlink, and the uplink communication and
the downlink communication are multiplexed in time domain.

[0067] FIG. 7 illustrates the allocation of subframes in the downlink of
in FDD mode. In FIG. 7, the subframes are allocated in one radio frame.
In the following explanation, the downlink subframe may be expressed as a
"DL subframe".

[0068] In the downlink of FDD mode, DL subframe (unicast) or DL subframe
(MBSFN) is transmitted from a base station. DL subframe (unicast) is used
to transmit data to a target terminal equipment. DL subframe (MBSFN) is
used for multimedia broadcast and a broadcast service (multimedia
broadcast and multicast service (MBMS)). MBSFN refers to a MBMS single
frequency network. In the following explanation, DL subframe (unicast)
may be called "unicast subframe", and DL subframe (MBSFN) may be called
"MBSFN subframe".

[0069] In the downlink in FDD mode, unicast subframe is allocated in
subframes #0, #4, #5, and #9 in a radio frame. Furthermore, unicast
subframe or MBSFN subframe is allocated in subframes #1 #2, #3, #6, #7,
and #8 in the radio frame. For example, a base station determines whether
unicast subframe or MBSFN subframe is allocated in each of subframes #1
#2, #3, #6, #7, and #8.

[0070] FIG. 8 illustrates the allocation of subframes in TDD mode. In TDD
mode, downlink subframe (unicast subframe, MBSFN subframe), special
subframe, and uplink subframe may be accommodated in a radio frame.
Furthermore, LTE and LTE-Advanced provide seven uplink/downlink
configurations illustrated in FIG. 8 as the allocation pattern of unicast
subframe, MBSFN subframe, special subframe and uplink subframe.

[0071] For example, in the uplink/downlink configuration 0, unicast
subframe is allocated in subframes #0 and #5, special subframe is
allocated in subframes #1 and #6, and uplink subframe is allocated in
subframes #2 through #4 and #7 through #9. In the uplink/downlink
configuration 1, unicast subframe is allocated in subframes #0 and #5,
special subframe is allocated in subframes #1 and #6, uplink subframe is
allocated in subframes #2, #3, #7, and #8, and unicast subframe or MBSFN
subframe is allocated in subframes #4 and #9. For example, a base station
determines which uplink/downlink configuration is to be used. Also, in
TDD mode, for example, a base station determines which is to be
allocated, unicast subframe or MBSFN subframe, in a subframe in which
unicast subframe or MBSFN subframe may be selected,

[0072] FIG. 9 illustrates a structure of a special subframe. It is assumed
that a subframe includes 14 OFDM symbols (Nsym=14). In FIG. 9, DL
indicates a downlink, UL indicates an uplink, and GP indicates a guard
period.

[0073] Special subframe includes a downlink symbol, a guard period, and an
uplink symbol. The guard period is provided to switch from a downlink
reception mode to an uplink transmission mode in the terminal equipment
3. In LTE and LTE-Advanced, nine special subframe configurations
illustrated in FIG. 9 are provided as the allocation patterns of a
downlink symbol, a guard period, and an uplink symbol in a special
subframe.

[0074] For example, in the special subframe configuration 0, a downlink
symbol is allocated in symbol #0 through #2, a guard period is allocated
in symbol #3 through #12, and an uplink symbol is allocated in symbol
#13. For example, a base station determines which special subframe
configuration is to be used.

[0075] Thus, in FDD mode, each radio frame may include unicast subframe
and MBSFN subframe as illustrated in FIG. 7. Furthermore, in TDD mode,
each radio frame may include unicast subframe, MBSFN subframe, special
subframe, and uplink subframe as illustrated in FIG. 8.

[0076] However, the number of reference signal symbols allocated in a
subframe depends on the type of subframe. In addition, the number of
reference signal symbols allocated in the special subframe depends on the
special subframe configuration.

[0077] In the unicast subframe, as illustrated in FIG. 10A, a reference
signal is allocated in OFDM symbols #0, #4, #7, and #11. In FIGS.
10A-10C, the shaded area indicates a reference signal symbol allocated in
the subframe. When a reference signal is allocated in the OFDM symbol,
the reference signal symbols are allocated at the intervals of 6
subcarriers. Therefore, when OFDM signal of Nc subcarriers carries data,
4×(Nc/6) reference signal symbols are allocated in the unicast
subframe.

[0078] In the MBSFN subframe, as illustrated in FIG. 10B, a reference
signal is allocated only in OFDM symbol #0. Therefore, when OFDM signal
of Nc subcarriers carries data, 1×(Nc/6) reference signal symbols
are allocated in the MBSFN subframe.

[0079] In the special subframe, a reference signal is allocated in the
symbol to which a downlink is assigned in OFDM symbols #0, #4, #7, and
#11. Therefore, in the special subframe of the configurations 0 and 5, a
reference signal is allocated only in OFDM symbol #0 as illustrated in
FIG. 10B. In the special subframe of the configurations 1 through 3, and
6 through 8, a reference signal is allocated in OFDM symbols #0, #4, and
#7 as illustrated in FIG. 10C. In the special subframe of the
configuration 4, a reference signal is allocated in OFDM symbols #0, #4,
#7, and #11 as illustrated in FIG. 10A. Note that no reference signal
symbol is allocated in the uplink subframe.

[0080] In summary, the numbers of reference signal symbols allocated in
respective subframes are listed below. However, the number of reference
signals allocated in one OFDM symbol is Nc/6 regardless of the type of
subframe as described above with reference to FIGS. 10A-10C. Therefore,
the number of reference signal symbols allocated in a subframe is
proportional to the number of OFDM symbols in which the reference signal
symbols are allocated in the subframe. That is, the number of reference
signal symbols allocated in a subframe uniquely corresponds to the number
of OFDM symbols in which the reference signal symbols are allocated in
the subframe. Therefore, in this example, the number of reference signal
symbols allocated in a subframe refers to the number of OFDM symbols in
which a reference signal symbol is allocated in the subframe.

[0081]
unicast subframe: 4

[0082] MBSFN subframe: 1

[0083] special subframe
(configurations 0, 5): 1

[0084] special subframe (configuration 1, 2, 3,
6, 7, 8): 3

[0085] special subframe (configuration 4): 4

[0086] uplink
subframe: 0

[0087] The RSRP measurement unit 17 of the terminal equipment 3 measures
RSRP considering the number of reference signal symbols allocated in each
subframe as described later in detail. Therefore, the RSRP measurement
unit 17 is provided with the information for specifying the allocation of
the reference signal symbol.

[0088] The base station 2 transmits a control signal including the
information for specifying the allocation of the reference signal symbol
to the terminal equipment 3 located in the cell. The control signal
includes, for example, the following information.

[0089] (1)
uplink/downlink configuration

[0090] (2) MBSFN subframe configuration

[0091] (3) special subframe configuration

[0092] The uplink/downlink configuration specifies the allocation pattern
of the unicast subframe, the MBSFN subframe, the special subframe, and
the uplink subframe as described above with reference to FIG. 8. The
MBSFN subframe configuration specifies the position in which the MBSFN
subframe is allocated as described above with reference to FIGS. 7 and 8.
The special subframe configuration specifies the allocation pattern of
the downlink symbol, the guard period, and the uplink symbol as described
above with reference to FIG. 9. Note that the base station 2 may notify
the terminal equipment 3 of the information for specification of FDD mode
or TDD mode.

[0093] Described next is the method of notifying the terminal equipment 3
of the configuration information from the base station 2. In this method,
it is assumed that a communication is performed in LTE or LTE-Advanced.

[0095] PBCH is allocated in subframe #0 in each radio frame. Specifically,
PBCH is fixedly allocated in the central 72 subcarriers in the symbols in
which PDCCH is allocated. Therefore, PBCH is allocated fixedly every 10
ms as illustrated in FIG. 12. When starting the communication with the
base station, the terminal equipment first receives PBCH to acquire
master information block (MIB). By so doing, the terminal equipment can
receive PDSCH by acquiring the information included in NIB.

[0096] The terminal equipment receives PDSCH allocated in subframe #5 at
the 20 ms interval. In this area, system information block type 1 (SIB1)
message is allocated. After acquiring SIB1 message, the terminal
equipment acquires SIB2 through SIB13 messages. The positions where SIB2
through SIB3 messages are allocated are described in SIB1 message. SIB is
described in, for example, 3GPP TS36.331 V10.5.0.

[0097] In TDD mode, information element TDD-Config is described in SIB1
message. TDD-Config includes subframeAssignment field indicating
uplink/downlink configuration and specialSubframePatterns field
indicating special subframe configuration. subframeAssignment specifies
any value of 0 through 6. specialSubframePatterns specifies any value of
0 through 8.

[0098] SIB2 message describes information element MBSFN-SubframeConfig.
MBSFN-SubframeConfig includes a field describing the information about
the allocation of MBSFN subframe. That is, MBSFN-SubframeConfig includes
a field describing the interval at which a radio frame including MBSFN
subframe appears, and the allocation of MBSFN subframe in the radio
frame. The allocation of MBSFN subframe in the radio frame is expressed
by 6 bits. In the field of the 6 bits, the subframe corresponding to the
bit where "1" is set is used as MBSFN subframe. In FDD mode, each bit
indicates the state of subframes #1, #2, #3, #6, #7, and #8 in order from
the most significant bit. In TDD mode, each bit indicates the state of
subframes #3, #4, #7, #8, and #9 in order from the most significant bit.
Note that in TDD mode, the least significant bit is not used.

[0099] As described above, the base station 2 transmits the control signal
including the above-mentioned three pieces of configuration information.
Then, the terminal equipment 3 located in the cell of the base station 2
periodically receives the control signal.

[0100] The terminal equipment 3 demodulates and decodes the control signal
received from the base station 2, and acquires the above-mentioned three
pieces of configuration information. The demodulation and decoding of the
control signal are performed by, for example, the data receiver 13
illustrated in FIG. 3. In this case, the acquired configuration
information is supplied from the data receiver 13 to the RSRP measurement
unit 17. The configuration information may be regenerated in the
measurement unit 16 from the control signal.

[0101] The received signal is fed to the RSRP measurement unit 17 as
illustrated in FIG. 6. The received signal is a frequency domain signal
output from the FFT unit 12 (that is, Nc modulated signals). Then, the
RSRP measurement unit 17 measures the power of the reference signal
symbol included in the received signal according to the configuration
information received from the base station 2.

[0102] The configuration information includes the information which
specifies the following (1) through (3).

[0103] (1) Allocation pattern of
unicast subframe, MBSFN subframe, special subframe, and uplink subframe
in a radio frame (refer to FIG. 8)

[0104] (2) Position where MBSFN
subframe is allocated in the radio frame (refer to FIGS. 7 and 8)

[0105]
(3) Allocation pattern of downlink symbol, guard period, and uplink
symbol in the special subframe (refer to FIG. 9)

[0106] Furthermore, it is assumed that the RSRP measurement unit 17
recognizes a multiplexing mode (TDD or FDD) of multiplexing the uplink
and the downlink by the notification from the base station 2.

[0107] Accordingly, the RSRP measurement unit 17 can detect the allocation
of the reference signal symbol in each received subframe. Furthermore,
the RSRP measurement unit 17 can detect the number of reference signal
symbols in each received subframe (or the number of OFDM symbols in which
the reference signal symbol is allocated in each received subframe).

[0108] Described next is the operation of the RSRP measurement unit 17.
The divider 21 divides a received signal into small sections and
sequentially distributes them to the plurality of measurement units 22
(22-1 through 22-n). The length of each small section is determined so
that, for example, a noise suppression effect described above with
reference to FIG. 4 is obtained. However, if the length of the small
section is too long, the measurement error becomes large when the
terminal equipment 3 moves at a high speed as described above with
reference to FIG. 5. Therefore, it is preferable that the length of the
small section is appropriately determined with these factors taken into
account. As an example, the length of the small section corresponds to
the period of 0.5 through several subframes.

[0109] Each measurement unit 22 measures the power of the reference signal
symbol included in the received signal distributed from the divider 21.
That is, the measurement unit 22 measures RSRP based on the reference
signal symbol included in the received signal in the small section. The
received signal in one small section includes a plurality of reference
signal symbols. Thus, RSRP calculated by the measurement unit 22 is
expressed by the following formula. (The following equation is an example
of a method for calculating RSRP, and is not limited to the method.)

RSRP=|h'|2

h'=Σ(Ai+jBi)/k

Ai+jBi indicates the channel state (or the reception state of
the i-th reference signal symbol) obtained by the i-th reference signal
symbol, k indicates the number of reference signal symbols, and h'
indicates an average channel state.

[0110] Therefore, the measurement units 22-1 through 22-n measure RSRP1
through RSRPn, respectively. The measurement units 22-1 through 22-n
measure corresponding RSRP in different small sections. That is, the
measurement units 22-1 through 22-n measure RSRP1 through RSRPn
corresponding to different small sections.

[0111] Thus, each measurement unit 22 measures RSRP based on the reference
signal symbols in the small section. Therefore, the "small section"
corresponds to "measurement period" for measurement of RSRP.

[0112] The weight coefficient calculator 23 calculates weight coefficients
W1 through Wn corresponding to RSRP1 through RSRPn measured by the
measurement units 22-1 through 22-n. The weight coefficients W1 through
Wn are determined based on the number of reference signal symbols in the
measurement periods of the measurement units 22-1 through 22-n. In this
case, the weight coefficient calculator 23 determines the weight
coefficients W1 through Wn so that, for example, the weight of the
measurement value obtained in the measurement period in which there is a
small number of reference signal symbols may be small, and the weight of
the measurement value obtained in the measurement period in which there
is a large number of reference signal symbols maybe large. An embodiment
of the method for determining the weight coefficients W1 through Wn is
described later.

[0113] The weighted average calculator 24 calculates a weighted average
using the weight coefficients W1 through Wn calculated by the weight
coefficient calculator 23 with respect to RSRP1 through RSRPn measured by
the measurement units 22-1 through 22-n. Then, the RSRP measurement unit
17 outputs the calculation result of the weighted average calculator 24
as RSRP to be reported to the base station 2.

[0114] Thus, the RSRP measurement unit 17 measures RSRP in a plurality of
measurement periods. Then, the RSRP measurement unit 17 calculates the
weighted average of the plurality of RSRP measurement values (that is,
RSRP1 through RSRPn) using the weight coefficients W1 through Wn.

[0115] The RSRP measurement value obtained in each measurement period is
calculated based on a plurality of reference signal symbols in the
measurement period. For example, assume that the received signal of the
measurement period 1 is the subframe illustrated in FIG. 10A, and the
received signal of the measurement period 2 is the subframe illustrated
in FIG. 10B. In this case, in the measurement period 1, RSRP1 is
calculated from the reference signal symbols allocated in OFDM symbol #0,
#4, #7, and #11. That is, RSRP1 is calculated from the reference signal
symbols allocated at four different time points. On the other hand, in
the measurement period 2, RSRP2 is calculated from the reference signal
symbols allocated in OFDM symbol #0. That is, RSRP2 is calculated from
the reference signal symbols allocated at one time point. Here, the
measurement accuracy or reliability in the measurement period where there
are a large number of reference signal symbols is high, and the
measurement accuracy or reliability in the measurement period where there
are a small number of reference signal symbols is low. Thus, in this
example, the measurement accuracy or reliability of RSRP1 is higher
compared with that of RSRP2.

[0116] For the reasons above, the weight coefficients W1 through Wn may be
determined so that the weight of the measurement value obtained in the
measurement period in which there is a small number of reference signal
symbols is small, and the weight of the measurement value obtained in the
measurement period in which there is a large number of reference signal
symbols is large. Therefore, if the weighted average of RSRP1 through
RSRPn is calculated using the weight coefficients W1 through Wn, the
contribution of a highly reliable RSRP measurement value becomes high,
and the contribution of a less reliable RSRP measurement value becomes
low. As a result, the reliability of RSRP obtained by the weighted
average is high.

[0117] If a propagation environment between the base station and the
terminal equipment is estimated in each measurement period, and a
weighted average is obtained so that the contribution of the RSRP
measurement value in the measurement period in which a propagation
environment is inferior may be smaller, then RSRP of high reliability may
be obtained. In this case, for example, the number of significant paths,
the standard deviation of desired wave power, the standard deviation of
SIR, a Doppler frequency, etc. are estimated as the propagation
environment. However, it is difficult to estimate the propagation
environment constantly with high accuracy. Therefore, when the estimation
accuracy of the propagation environment is low, the reliability of the
finally obtained RSRP is also low. Furthermore, since the process of
estimating the propagation environment is subject to computational
complexity, there is the possibility of large power consumption of the
terminal equipment.

[0118] On the other hand, in the method of the embodiments of the present
invention, the weight coefficients W1 through Wn are determined based on
the number of reference signal symbols in each measurement period.
Therefore, the computational complexity of the process of determining the
weight coefficients W1 through Wn is low, thereby requiring smaller power
consumption.

First Embodiment

[0119] In the first embodiment, the uplink and the downlink are
multiplexed in FDD mode. The RSRP measurement unit 17 measures RSRP from
six consecutive subframes. The length of each measurement period is "2
subframes". Therefore, in the RSRP measurement unit 17, three measurement
values (RSRP(1) through RSRP(3)) are obtained using three measurement
units 22 (that is, the measurement units 22-1 through 22-3 (n=3)).

[0120] The six subframes input to the RSRP measurement unit 17 are
"unicast", "MBSFN", "MBSFN", "MBSFN", "unicast", and "unicast". The
"unicast" indicates a unicast subframe, and the "MBSFN" indicates a MBSFN
subframe.

[0121] In this case, the "unicast" and "MBSFN" of the measurement period 1
are input to the measurement units 22-1. The "MBSFN" and "MBSFN" of the
measurement period 2 are input to the measurement units 22-2. The
"unicast" and "unicast" of the measurement period 3 are input to the
measurement units 22-3.

[0122] In the unicast subframe, as illustrated in FIG. 10A, a reference
signal is allocated in OFDM symbols #0, #4, #7, and #11. That is, in one
unicast subframe, 4×(Nc/6) reference signal symbols are allocated.
On the other hand, in the MBSFN subframe, as illustrated in FIG. 10B, a
reference signal is allocated only in OFDM symbol #0. That is, in one
MBSFN subframe, 1×(Nc/6) reference signal symbols are allocated.

[0123] Therefore, in the measurement period 1, there are 5×(Nc/6)
reference signal symbols. In addition, in the measurement period 2, there
are 2×(Nc/6) reference signal symbols. Furthermore, in the
measurement period 3, there are 8×(Nc/6) reference signal symbols.

[0124] In the first embodiment, the weight coefficient calculator 23 uses
the number of reference signal symbols in each measurement period as a
weight coefficient. However, Nc/6 is a constant, and common in the
measurement periods 1 through 3. Therefore, in the explanation below,
"Nc/6" is omitted. That is, the numbers of the reference signal symbols
in the measurement periods 1, 2, and 3 are represented by 5, 2, and 8,
respectively. Then, when the six subframes illustrated in FIG. 13 are
input to the RSRP measurement unit 17, the weight coefficient calculator
23 outputs W1=5, W2=2, and W3=8 respectively as the weight coefficients
corresponding to the measurement periods 1, 2, and 3.

[0125] The measurement unit 22-1 obtains the received power measurement
value RSRP(1) based on a plurality of reference signal symbols included
in the received signal of the measurement period 1. Similarly, the
measurement units 22-2 and 22-3 obtain the received power measurement
value RSRP(2) and RSRP(3), respectively.

[0126] The weighted average calculator 24 calculates RSRP of the received
signal by calculating a weighted average using the W1 through W3 for
RSRP(1) through RSRP(3). The weighted average in the first embodiment is
illustrated in FIG. 13.

[0127] Thus, in the first embodiment, the number of reference signal
symbols in a measurement period is used as a weight coefficient for the
measurement period. In this process, the measurement accuracy of RSRP in
each measurement period depends on the number of reference signal symbols
used in measurement. That is, the measurement accuracy in the measurement
period having a large number of reference signal symbols is high, and the
measurement accuracy in the measurement period having a small number of
reference signal symbols is low. Therefore, in calculating RSRP using the
weighted average according to the first embodiment, the influence of the
measurement value obtained in a measurement period having a small number
of reference signal symbols (the measurement period 2 in FIG. 13) is
small, and the influence of the measurement value obtained in a
measurement period having a large number of reference signal symbols (the
measurement period 3 in FIG. 13) is large. As a result, as compared with
the method in which no weighted average is used, the measurement accuracy
of RSRP is enhanced.

[0128] The number of reference signal symbols in a measurement period is
proportional to the number of OFDM symbols in which the reference signal
symbols are allocated in the measurement period. Therefore, substantially
the same calculation result of a weighted average is obtained when the
weight coefficients W1 through Wn are determined based on the "number of
the OFDM symbols in which the reference signal symbols are allocated in
the measurement period" instead of the "number of the reference signal
symbols in the measurement period". Therefore, in determining the weight
coefficients W1 through Wn, the "number of the reference signal symbols
in the measurement period" is equivalent to the "number of the OFDM
symbols in which the reference signal symbols are allocated in the
measurement period". In addition, in determining the weight coefficients
W1 through Wn, the "number of the OFDM symbols in which the reference
signal symbols are allocated in the measurement period" is one example of
the "number of the reference signal symbols in the measurement period".

Second Embodiment

[0129] In the first embodiment, the number of reference signal symbols in
each measurement period is used as a weight coefficient. On the other
hand, in the second embodiment, the square of the number of reference
signal symbols in each measurement period is used as a weight
coefficient.

[0130] As illustrated in FIG. 14, also in the second embodiment as in the
first embodiment, the numbers of the reference signal symbols in the
measurement periods 1, 2, and 3 are 5, 2, and 8, respectively. However,
in the second embodiment, the square of the number of reference signal
symbols in a measurement period is used as a weight coefficient.
Therefore, the RSRP measurement unit 17 in the second embodiment outputs
W1=52=25, W2=22=4, and W3=82=64 respectively as the weight
coefficients corresponding to the measurement periods 1, 2, and 3.

[0131] As in the first embodiment, the weighted average calculator 24
calculates RSRP by calculating the weighted average using W1 through W3
for RSRP(1) through RSRP(3). However, as described above, different
weight coefficients are used between the first and second embodiments.
The weighted average in the second embodiment is illustrated in FIG. 14.

[0132] Thus, in the second embodiment, the square of the number of
reference signal symbols in each measurement period is used as a weight
coefficient. Therefore, according to the weighted average according to
the second embodiment, as compared with the first embodiment, the
contribution of the measurement value obtained in the measurement period
(measurement period 2 in FIG. 14) in which the number of reference signal
symbols is small becomes further smaller, and the contribution of the
measurement value obtained in the measurement period (measurement period
3 in FIG. 14) in which the number of reference signal symbols is large
becomes further larger. Therefore, according to the method in the second
embodiment, as compared with the first embodiment, the measurement
accuracy of RSRP is further improved.

Simulation

[0133] FIG. 15 is an explanatory view of a simulation model for the
measurement accuracy of RSRP. In the simulation, RSRP is measured from
two subframes. The length of each measurement period is "one subframe".
That is, in the measurement periods and 2, the measurement values RSRP(1)
and RSRP(2) are calculated respectively. The two subframes input for RSRP
measurement are "unicast" and "MBSFN". Therefore, the number of reference
signal symbols in the measurement periods 1 and 2 are "4" an "1"
respectively. In this case, the accuracy or reliability of the
measurement value RSRP(2) is lower than the measurement value RSRP(1).
Furthermore, the terminal equipment which measures RSRP remains
stationary. The ideal value of RSRP when there is no noise is -70 dBm. In
the model above, RSRP is calculated in the following three methods.

[0134] In the "method without a weight", RSRP is calculated by a simple
average of RSRP(1) and (2).

[0135] The "method 1" corresponds to the first embodiment. RSRP(1) and
RSRP(2) are weight averaged according to the number of reference signal
symbols in a corresponding measurement period. The weight coefficients
W1=4 and W2=1 are assigned to RSRP(1) and RSRP(2), respectively.

[0136] The "method 2" corresponds to the second embodiment. RSRP(1) and
RSRP(2) are weight averaged according to the square of the number of
reference signal symbols in a corresponding measurement period. The
weight coefficients W1=42=16 and W2=12=1 are assigned to
RSRP(1) and RSRP(2), respectively.

[0138] In FIG. 16A, the "method without a weight" and the method 1 are
compared. In the measurement by the method 1 as compared with the "method
without a weight", there is a high probability that RSRP close to the
ideal value (-70 dBm) is obtained. That is, according to the method 1,
there is a low probability that RSRP having a large error with respect to
the ideal value is obtained.

[0139] In FIG. 16B, the "method without a weight" is compared with the
method 2. Also in this case, in the measurement by the method 2 as
compared with the "method without a weight", there is a high probability
that RSRP close to the ideal value is obtained.

[0140] In FIG. 16C, the method 1 and the method 2 are compared. As
compared with the method 1, there is a higher probability that RSRP close
to the ideal value is obtained in the method 2.

[0141] Thus, since the RSRP measurement unit 17 obtains a weighted average
using the number (or the square of the number) of the reference signal
symbols, the influence of the measurement period having low measurement
accuracy or reliability is reduced. As a result, as illustrated in FIGS.
16A and 16B, as compared with the "method without a weight", there is a
higher probability that RSRP close to the ideal value is obtained.

[0142] Described next is erroneous detection of a cell by a terminal
equipment. A terminal equipment periodically performs a cell search to
detect cell ID of a serving cell, and measures RSRP for the detected cell
ID. However, in the cell search, a cell maybe erroneously detected
although it does not actually exist. In this case, the terminal equipment
measures RSRP not only for an actual cell which actually exists but also
for a cell which actually does not exist.

[0143] In this case, if the averaging time for calculation of RSRP is
sufficiently long, RSRP of the non-existing cell becomes sufficiently
small. However, since the averaging time is finite, a value close to RSRP
of an actual cell may be detected as RSRP of a non-existing cell.

[0144] FIG. 17 illustrates the probability density function of RSRP
calculated in the method without a weight on a "actual cell" and a
"non-existing cell". In this case, the two probability density functions
largely overlap. In the RSRP area in which the two probability density
functions overlap, the terminal equipment is not able to decide whether
or not the detected cell is an "actual cell" or a "non-existing cell".

[0145] For example, it is assumed that "threshold: -72.5 dBm" is set to
detect an actual cell. In this case, when RSRP is higher than or equal to
-72.5 dBm, the terminal equipment decides that a signal is received from
an actual cell. On the other hand, when RSRP is smaller than -72.5 dBm,
the terminal equipment decides that there is no cell corresponding to the
received signal. Under this condition, when RSRP is measured by the
"method without a weight", the probability of erroneous detection (or
erroneous decision) is 27% according to the simulation. The erroneous
detection indicates detecting a "non-existing cell" as an actual cell.

[0146] FIG. 18 illustrates the probability density function of RSRP
calculated for the "actual cell" and the "non-existing cell" in the
"method 1 (first embodiment)". In this case, as compared with the example
illustrated in FIG. 17, the area where two probability density functions
overlap is small. As a result, when the threshold -72.5 dBm is set, the
erroneous detection probability is reduced to about 0.6%.

[0147] FIG. 19 illustrates the probability density function of RSRP
calculated for the "actual cell" and the "non-existing cell" in the
"method 2 (second embodiment)". In this case, as compared with the
example illustrated in FIG. 18, the area where two probability density
functions overlap is further smaller. As a result, when the threshold
-72.5 dBm is set, the erroneous detection probability is reduced to
approximately 0%.

Handover

[0148] The terminal equipment measures RSRP of a serving cell and an
adjacent cell, and reports the measurement result to a serving base
station. The serving base station compares RSRP between the serving cell
and the adjacent cell based on the report from the terminal equipment.
Then, the serving base station performs a handover from the serving cell
to the adjacent cell when, for example, RSRP of the adjacent cell is
larger than RSRP of the serving cell.

[0149] FIGS. 20A and 20B illustrate examples of a handover operation based
on RSRP. In FIGS. 20A and 20B, the curve in solid line and the curve in
broken line indicate actual RSRP of the serving cell and the adjacent
cell, respectively. The square symbols and triangle symbols respectively
indicate RSRP measured with respect to the serving cell and the adjacent
cell by the terminal equipment. The deviation between the curve in solid
line and the square symbol and the deviation between the curve in broken
line and the triangle symbol correspond to measurement error.

[0150] At time T1, the terminal equipment receives a radio signal from
both the serving base station and the base station of the adjacent cell.
In this case, in the terminal equipment, RSRP of the serving cell is
larger than RSRP of the adjacent cell. Afterwards, it is assumed that the
terminal equipment moves in the direction toward the base station of the
adjacent cell. That is, after the time T1, RSRP of the serving cell
gradually decreases in the terminal equipment, and RSRP of the adjacent
cell gradually increases. Then, at time Tx, it is assumed that RSRP of
the adjacent cell exceeds RSRP of the serving cell.

[0151] FIG. 20A indicates the handover control when RSRP of low
measurement accuracy is reported to the base station. In this example, at
time T2, the measurement value of RSRP of the adjacent cell exceeds the
measurement value of RSRP of the serving cell. Therefore, when the
measurement result is reported, the serving base station performs a
handover from the serving cell to the adjacent cell.

[0152] Afterwards, at time T3, the measurement value of RSRP of the
serving cell exceeds the measurement value of RSRP of the adjacent cell.
Therefore, when the measurement result is reported, the handover is
performed again.

[0153] Similarly, each time the comparison results between the two
measurement values of RSRP becomes inverted, a handover is performed. In
FIG. 20A, the terminal equipment is connected to the serving cell in the
time period S, and the terminal equipment is connected to the adjacent
cell in the time period indicated by diagonal lines. Thus, when the
measurement accuracy of RSRP in the terminal equipment is low, the
handover is performed plural times when the difference in RSRP is small
between the serving cell and the adjacent cell, thereby causing unstable
communication state.

[0154] FIG. 20B indicates the handover control when RSRP of high
measurement accuracy is reported to the base station. In this example,
during period T1 through T4, the measurement value of RSRP of the serving
cell continuously exceeds the measurement value of RSRP of the adjacent
cell. Then, at time T4, the measurement value of RSRP of the adjacent
cell exceeds the measurement value of RSRP of the serving cell, and a
handover is performed. The time T4 is close to time Tx. That is, when the
measurement accuracy of RSRP is high, a handover is performed with
appropriate timing, thereby maintaining stable communication state during
the handover.

[0155] Thus, if the measurement accuracy of RSRP is improved, the
communication becomes stable during the handover. Therefore, if RSRP is
measured in the method adopted in the RSRP measurement unit 17 according
to the above-mentioned embodiments, the communication maintains a stable
communication state.

Other Embodiments

[0156] The length of the measurement period in which the measurement unit
22 measures RSRP is one subframe or two subframes in the embodiments
above, but the present invention is not limited to these lengths. That
is, the measurement period may be shorter than the subframe time.

[0157] With the configuration illustrated in FIG. 6, a plurality of RSRP
measurement values are generated using a plurality of measurement units
22 (22-1 through 22-n), but the present invention is not limited to this
configuration. That is, the measurement units 22 may sequentially
generate a plurality of RSRP measurement values.

[0158] In the explanation above, the measurement unit 22 generates a
received power value indicated by real number, but the present invention
is not limited to this implementation. For example, the measurement unit
22 may output a correlation value among a plurality of channel states
h1, h2, h3, . . . which are estimated from a plurality of
reference signal symbols allocated in the measurement period. The
correlation value is calculated by, for example, multiplying a complex
number indicating a channel state by a complex conjugate of a complex
number indicating another channel state. In this case, the correlation
value is expressed by a complex number. However, when the measurement
period is sufficiently short, the correlation value is substantially
equal to the received power of the reference signal symbol. Therefore,
the value obtained by expressing the result of calculating a weighted
average after the weighted average calculator 24 calculates the weighted
average of a plurality of correlation values is substantially equal to
RSRP calculated by the weighted average calculator 24 when the
measurement unit 22 generates a received power value expressed by real
number. Therefore, in the process of calculating RSRP, the correlation
value of the channel state is one example of a received power value.

[0159] All examples and conditional language provided herein are intended
for the pedagogical purposes of aiding the reader in understanding the
invention and the concepts contributed by the inventor to further the
art, and are not to be construed as limitations to such specifically
recited examples and conditions, nor does the organization of such
examples in the specification relate to a showing of the superiority and
inferiority of the invention. Although one or more embodiments of the
present invention have been described in detail, it should be understood
that the various changes, substitutions, and alterations could be made
hereto without departing from the spirit and scope of the invention.